PROJECT SUMMARY/ABSTRACT: Pancreatic ductal adenocarcinoma (PDAC) remains a major therapeutic challenge due to its innate and acquired chemoresistance. To date, the addition of targeted molecular therapies to cytotoxic compounds has failed to show any significant improvement in increasing overall survival in PDAC. Hence, there is a desperate need to develop novel therapeutic approaches that both reduce the PDAC tumor burden and improve overall survival without producing significant off-target effects. We have shown that Urolithin A (Uro A), a novel natural dietary microflora-derived metabolite, mediates its anti-tumor activities by inhibiting immunosuppressive cells. A Phase I clinical trial of Uro A demonstrates that it is well-tolerated with good bioavailability. The relative superiority of Uro A to cytotoxic chemotherapy in our preclinical study highlights the need to study Uro A as a chemopreventive agent. Uro A treatment alone increased T-cell infiltration to the tumor while decreasing the overall number of intratumoral myeloid derived suppressor cells and immunosuppressive regulatory T cells. Tumor suppressive effect of Uro A is T cell dependent and is accompanied by sustained PD-L1/PD-1 expression. Immune therapies targeting the checkpoint inhibitors (CPI) such as PD-1 and/or CTLA-4 can enhance the T cell response to tumors and these inhibitors have shown great success in clinic. Therefore, we hypothesize that the addition of an anti-PD1 and/or anti-CTLA-4 therapy to Uro A combination will allow assessment of its effects on the tumor microenvironment and overall response rate. We further hypothesized that CPI unmasks clinical responses to Uro A and that enhanced T cell responses with this regimen may ultimately be limited by the increased activity of immune TME. We will test these hypotheses in two aims with pre-clinical murine models. Aim 1: Evaluate the impact of combined Uro A treatment and checkpoint inhibition on stromal and immune microenvironment in PDAC in vivo. We will determine the immune predictors of responses and profile the phenotypes of various immune cell subsets from treatment groups. Aim 2: Determine if checkpoint inhibition together with Uro A will improve survival in mouse model of PDAC. Genetic mice will be treated with Uro A followed by anti- PD1 and/or anti-CTLA-4 antibodies to determine efficacy of the treatment response. This project will elucidate a mechanistic understanding of the impact of a chemopreventive agent and CPI on PDAC, facilitating the development of optimal combinatorial therapy for PDAC. Success in these pre-clinical models would then facilitate rapid translation of this work into clinical trials.